The present invention relates generally to the field of microwave circuits, and more particularly to integrated thick film RF and microwave microcircuit modules, and even more particularly to micro-switches and heaters within such modules.
Electronic circuits of all construction types typically have need of switches and relays. The typical compact, mechanical contact type relay is a lead relay. A lead relay comprises a lead switch, in which two leads composed of a magnetic alloy are contained, along with an inert gas, inside a miniature glass vessel. A coil for an electromagnetic drive is wound around the lead switch, and the two leads are installed within the glass vessel as either contacting or non-contacting.
Lead relays include dry lead relays and wet lead relays. Usually with a dry lead relay, the ends (contacts) of the leads are composed of silver, tungsten, rhodium, or an alloy containing any of these, and the surfaces of the contacts are plated with rhodium, gold, or the like. The contact resistance is high at the contacts of a dry lead relay, and there is also considerable wear at the contacts. Since reliability is diminished if the contact resistance is high at the contacts or if there is considerable wear at the contacts, there have been various attempts to treat the surface of these contacts.
Reliability of the contacts may be enhanced by the use of mercury with a wet lead relay. Specifically, by covering the contact surfaces of the leads with mercury, the contact resistance at the contacts is decreased and the wear of the contacts is reduced, which results in improved reliability. In addition, because the switching action of the leads is accompanied by mechanical fatigue due to flexing, the leads may begin to malfunction after some years of use.
A newer type of switching mechanism is structured such that a plurality of electrodes are exposed at specific locations along the inner walls of a slender sealed channel that is electrically insulating. This channel is filled with a small volume of an electrically conductive liquid to form a short liquid column. When two electrodes are to be electrically closed, the liquid column is moved to a location where it is simultaneously in contact with both electrodes. When the two electrodes are to be opened, the liquid column is moved to a location where it is not in contact with both electrodes at the same time.
To move the liquid column, Japanese Laid-Open Patent Application SHO 47-21645 discloses creating a pressure differential across the liquid column is created. The pressure differential is created by varying the volume of a gas compartment located on either side of the liquid column, such as with a diaphragm.
In another development, Japanese Patent Publication SHO 36-18575 and Japanese Laid-Open Patent Application HEI 9-161640 disclose creating a pressure differential across the liquid column by providing the gas compartment with a heater. The heater heats the gas in the gas compartment located on one side of the liquid column. The technology disclosed in Japanese Laid-Open Patent Application 9-161640 (relating to a microrelay element) can also be applied to an integrated circuit. Other aspects are discussed by J. Simon, et al. in the article xe2x80x9cA Liquid-Filled Microrelay with a Moving Mercury Dropxe2x80x9d published in the Journal of Microelectromechanical Systems, Vol.6, No. 3, Sep. 1997. Disclosures are also made by You Kondoh et al. in U.S. Pat. No. 6,323,447 entitled xe2x80x9cElectrical Contact Breaker Switch, Integrated Electrical Contact Breaker Switch, and Electrical Contact Switching Methodxe2x80x9d.
Speed of operation, power requirements for switching, and switching reliability are all important considerations for such switches. Repeated switching cycles have been found to result in the occurrence of short circuits. A possible cause for these short circuits is the increased wetting of the material surface by the mercury caused by the formation of microcracks in the material due to the repeated exposure of the material to the high temperatures experienced during the switching process. Thus, it would be advantageous to provide techniques which would reduce the amount of heat dissipated in the walls of the material surrounding the liquid metal, while increasing the speed of switching.
An apparatus for separating a liquid in a liquid metal micro-switch is disclosed in representative embodiments. The apparatus comprises a heater and a sub-channel inside a structure. The heater is located inside a cavity of the structure onto which the liquid metal micro-switch is fabricated. The sub-channel inside the structure connects the cavity to a main channel. The sub-channel has a cross-sectional area. The value of the cross-sectional area at the boundary between the sub-channel and the main channel is less than the value of the cross-sectional area at the boundary between the sub-channel and the cavity. The gas permeates the cavity and the sub-channel and is capable of extending into the main channel.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.